Q44Short answer
The enthalpy of reaction for the reaction : –1 2H2(g) + O2(g) → 2H2O(l) is ∆rHV = – 572 kJ mol . What will be standard enthalpy of formation of H2O (l ) ?
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According to the definition of standard enthalpy of formation, the enthalpy change for the following reaction will be standard enthalpy of formation of H2O (l) H2(g) + O (g) → H2O(l ). 2 2 or the standard enthalpy of formation of H2O(l ) will be half of the enthalpy of the given equation i.e., ∆rH is also halved. –1 V 1 V − 572 kJ mol ∆f H H O(l ) = × ∆r H = = – 286 kJ/mol. 2 2 2